1. Field of the Invention
The present invention relates to an image reading apparatus that reads an original by illuminating the original, and an image forming apparatus including the image reading apparatus.
2. Related Art
An image reading apparatus of this type reads an original, and is used independently or being provided in a copier or the like. When used independently, the read original image is outputted to an external printer or the like, and when used being provided in a copier, the read original image is copied by the copier.
Such an image reading apparatus is provided with an original guide plate made of, for instance, a glass plate having translucency and a reading scanner disposed under the original guide plate, and reads an original on the original guide plate by illuminating the original using the reading scanner while transporting the original so as to cause the original to pass over the original guide plate. The reading scanner has a light source that illuminates an original, and an image sensor (such as a CCD) that photoelectrically converts the light reflected from the original.
Here, if the transported original is caught at an edge portion of the original guide plate, a jam occurs. Accordingly, an inclined surface (C surface (chamfer surface)) is formed at the edge portion of the original guide plate, thereby promptly guiding the original from the inclined surface at the edge portion of the original guide plate onto the upper surface of the original guide plate.
However, the inclined surface of the original guide plate is ground glass-like, and thus the original is chipped by the ground glass-like inclined surface, thereby generating a large amount of paper powder, or the illumination light from the reading scanner is diffused by the ground glass-like inclined surface, thereby causing an insufficiency of the illumination light for the original.
For example, in JP H09-93405A, the unevenness and insufficiency of illumination light is prevented by polishing a C surface of a transparent original stage until it becomes transparent. If the C surface of the original stage is polished until it becomes transparent, the original will not be chipped by the C surface.
However, if the C surface of the original stage is polished until it becomes transparent as in JP H09-93405A described above, the cost of the original stage is greatly increased. This is because the C surface of the original stage is originally ground glass-like, and thus a polishing process and a time period for this process will be separately necessary in order to polish the C surface until it becomes transparent.